#define _CRT_SECURE_NO_WARNINGS 1
#include"_string.h"
#include<vector>
int main()
{
    int n;
    cin >> n;
    if (n == 0)return 0;
    if (n == 1 || n == 2)return 1;
    vector<int> dp(n + 1);
    dp[0] = 0; dp[1] = 1; dp[2] = 1;
    for (int i = 3; i < n + 1; i++)
        dp[i] = dp[i - 3] + dp[i - 2] + dp[i - 1];
    cout<< dp[n]<<endl;
	return 0;
}